New EHV trends and adoption in Nepal

EHV (Extra High Voltage) systems work at about 300–765 kV AC, and UHV above that. Worldwide, power systems are changing because of the need to carry large amounts of renewable power over long distances, to control power flow, and to make the grid smart and reliable.

New trends in EHV systems worldwide

1. Higher voltages (UHV AC and DC): China uses 1000 kV AC and ±800 to ±1100 kV DC lines carrying 8–12 GW over 2000–3000 km. India has 765 kV AC and ±800 kV DC.
2. HVDC and VSC-HVDC: voltage-source converters (MMC) allow multi-terminal DC grids, offshore wind connection and black-start ability.
3. FACTS devices: SVC, STATCOM, TCSC, UPFC increase line loading, control voltage and damp oscillations.
4. Compact and high-capacity lines: bundled conductors, compact towers, HTLS (high temperature low sag) conductors for re-conductoring, and multi-circuit towers to save right-of-way.
5. Gas-insulated substations (GIS) and GIL: SF6 or SF6-free (clean-air, g³) insulation in small space; very useful in hilly or urban areas.
6. Underground and submarine XLPE cables at 400–525 kV.
7. Smart grid and digital substations: IEC 61850, PMU-based wide-area monitoring (WAMS), SCADA/EMS, dynamic line rating, digital protection.
8. Renewable integration and storage: large solar/wind parks, pumped storage and battery storage connected through EHV networks.
9. Regional interconnections and power trading: cross-border grids (e.g. Europe, SAARC/BBIN) and electricity markets.

How Nepal can adopt them

• 400 kV backbone: complete the east–west 400 kV corridor (Inaruwa–Dhalkebar–Hetauda–Butwal and beyond) and north–south 400 kV corridors from hydropower areas (Koshi, Kaligandaki, Karnali) to load centres and border points.
• Cross-border links: strengthen 400 kV links with India (Dhalkebar–Muzaffarpur, New Butwal–Gorakhpur) and plan links with China and Bangladesh to export surplus wet-season hydropower.
• HVDC for export: for large storage and export projects in the far west or east (several GW over long distance to Indian load centres), an HVDC or HVDC back-to-back link will allow controlled trading and asynchronous operation.
• FACTS: STATCOM/SVC at weak substations to hold voltage on long radial lines and lightly loaded 220/400 kV lines in the dry season.
• GIS substations in narrow valleys and Kathmandu, where land is scarce.
• HTLS re-conductoring of old 132 kV lines to raise capacity without new right-of-way.
• Smart grid: expand SCADA/load dispatch, PMUs, smart meters and automation in NEA's network to cut losses and outages.
• Storage and solar: pumped-storage and reservoir projects plus solar to balance the run-of-river surplus/deficit.
• Capacity building: training of engineers, national grid code, and private/foreign investment through clear policy.

By adopting these trends, Nepal can evacuate its hydropower reliably, reduce spill in the wet season and earn from regional power trade.